Inserts for rock drill bits



Aug. 25, i964 H. H. scHLosslN 3,M5,79

INSERTS FOR ROCK DRILL BITS Filed Dec. 19, 1962 Hrrsf United States Patent O This invention relates to rock drill bits of the kind including a chisel-shaped insert of hard metal secured within a slot in the bit. The main accent of the invention is on bits having a single insert (integral or builttop of the insert. Coupled with increased durability is an increase in penetration speed.

The invention is further discussed with reference to the accompanying drawings, in which FIGURE 1 is a side elevation of a standard insert;

FIGURE 2 is a side elevation of an insert according to the teachings of the prior art;

FIGURE 3 is a section on the line 2 2 of FIGURE 2;

FIGURE 4 is a plan View of FIGURE 1;

FIGURE 5 is a side elevation of one embodiment of the invention;

FIGURE 6 is a section on the line 5 5 of FIG- URE 5;

FIGURE 7 is a plan view of FIGURE 4;

up), but it is also applicable to bits having inserts spaced FIGURE 8 is a side elevation of the preferred emb0diin cruciform formation or any formation with more ment; than one cutting insert. FIGURE 9 is a section on the line 8 8 of FIGURE The present application is a continuation-in-part of 8; and application No. 32,940 led on May 31, 1960, and FIGURE 10 is a plan view of FIGURE 7. abandoned on the filing of the present application. In FIGURES 2 to 10 similar parts have been desig- With the advent of cemented tungsten carbide (usually nated by the same reference numbers. Thus in each vknown as hard metal) percussive rock drilling has been case there is a substantially rectangular prismatic body improved beyond recognition. However, hard metal is 10 with reaming ends 11 which are curved about the anexpensive material and the aim of manufacturers is centre of the insert and inclined towards the base 12 to increase the utility of the material. It is believed in a well known manner. that the optimum in relation to the composition of hard Each insert has a cutting end comprising a cutting metals has almost been reached. edge 13, snubs 14 to either end of the edge 13, substan- In regard to the shape of the cemented tungsten tially triangular faces 15 with their apices at the cutting carbide bits a lot of work has been done, but over many edge and broadening towards and into the snubs 14 and years shape has been more or less standardized as that lands 16 iianking the cutting edge 13. shown in FIGURE l. The standard shape is a chisel In each case also the lands 16 are concave as can be shape which has been used also for steel drilling edges. seen from the drawings.

Applicant is aware of the fact that a departure from In FIGURES 2 to 4, the faces 15 constitute a prothe standard shape has been proposed in the prior art. gressive broadening of the edge 13 towards the teaming In the latter case it was proposed that cutting wings have ends 11. As seen from FIGURE 4, the cutting edge iiattened forward faces or in other words the cutting and the faces 15 are in the same plane. The cutting edges progressively broadened from the centre towards edge is, therefore, a straight line flanked by triangular the reaming ends. The greater amount of material presflats. ent at the outer ends of the wings where abrasion is In the embodiments of FIGURES 5 to 7 and 8 to 10 greatest due to the greater volume broken per revoluthe cutting edge 13 is concave below shoulders 18 at the tion is said to make the bit more durable. Applicant junctions of the faces 15 and the snubs 14. In each has tested the teaching of this prior art on tungsten case the insert is 1.441 inches wide (at its maximum carbide inserts and has found that greater durability width), 0.398 inch thick and 0.625 inch high. The main as compared to a standard chisel-shape in fact results. difference lies in the depth of the concavity of the cut- The present invention is based on the unexpected disting edge below the shoulders 18. In the case of the covery that durability may be increased still further if embodiment of FIGURES 5 to 7 it is 0.019 inch the cutting edge is anked by concave lands arranged and in the case of preferred embodiment 0.059 inch. to intersect (the cutting edge being the intersecting line) With wider bits a depth of 0.080 inch has given good a distance of preferably at least 0.019 inch below the results.

Table l Flat top Shallow saddle Deep saddle Standard Progressive Gauge Pen. Gauge Pen. Gauge Pen. Gauge Pen.

loss, speed, loss, speed, loss, speed, loss, speed, mm. ins/min. mm. ins/min. mm. ins/min. mm. ins/min.

Fedriiled;

3 .o3 12. 50 .o3 12. 63 .02 12. 70 .03 12.63 12. 37 .06 12.57 .04 12. 63 .06 12.57 12. 24 .o9 12.44 .06 12. 5o 1o 12.37 12. 12 13 12.37 .os 12. 50 14 12. 24 12. 06 .17 12. 24 .1o 12.50 17 12.24 12.06 .19 12.18 .12 12.44 .2o 12.00 12.00 .20 12. 06 .14 12.37 .23 11.76 11. ss .23 12.12 17 12.31 .27 11.54 11. 32 .25 12. 0o .19 12.37 .30 11. 37 11. 38 .23 12.00 .21 12.24 .33 11.27 11.70 .30 11. 82 .24 12.24 .36 11.16 11.65 .32 11.71 .26 12.31 .39 11.00 11.59 .35 11. .28 12.18 .42 10.85 11.54 39 11.65 .31 12. 0s .45 10. 71 11.54 .43 11. 54 .35 11. 88 .49 10.43

In Table I gauge loss has been chosen as a measure 10 of durability. A small gauge loss means good durability. Gauge loss is the amount by which the overall distance between the reaming ends 11 is decreased. Cumulative iigures have been given in Table I. After the first three l5 feet or after the first hole the gauge loss was 0.03 mm. in three cases and 0.02 mm. in the case of the deep saddle and so on. In the tests which led to Table I there was no resharpening and, as can be seen, fifteen holes were drilled in each case.

The hole depth in each case was 3'0".

The term penetration speed as used in Table I means the number of inches that the-bit penetrated per minute of drilling time.

The values are averages of inserts of each type that 25 were used in the tests.

As t0 durability the figures clearly show that the embodiments of the invention have an advantage over the standard and the flat top. The same applies to penetration speed.

3 In another test the standard and the deep saddle were 0 run against each other to the end of their respective useresharpening. Wear resistance is calculated by multiplying the number of holes drilled with 3.5 feet and dividing that by the overall decrease in length.

As pointed out above a reason why the flat top should give better results than the standard bit is given in the prior art. However, there is no apparent reason why the teachings of the present invention should provide any advantages over the at top'. This much is clear: the advantages do exist. In the course of actual drilling on the South African gold mines with drills equipped with the deep saddle a practical problem was encountered as a result of these improved results. It was found that higher water pressures were needed to carry away the cuttings that were formed with the deep saddle to prevent the drill from sticking in the hole.

I claim:

1. An insert for a percussive rock drill bit comprising an elongated substantially rectangular prismatic configuration and having a at base; two opposed at sides at right angles to the base; two opposed substantially parallel reaming ends at right angles to the base and the long axis of the insert; and a substantially chisel-shaped cutting formation opposed to the base, the cutting formation consisting in inclined concave lands meeting at a short axis of the insert and intersecting the flat sides, a concave cutting edge being formed where the concave lands meet and such cutting edge broadening into a pair of divergent triangular faces continuous with and having the same concavity as the cutting edge, and a pair of inclincd snubs joining the bases of the triangular faces with the reaming ends, a shoulder being formed by the base of each of the triangular faces merging with the upperful lives. The results are tabulated below in Table II. most portion of each snub.

Table Il Hole 1 15* 16 30* 31 45* 46 i 60* 61 i 75* 76 90* 91 105 Penetration speed, in /mn Standard 7. 7 7. 1 9. 0 7. 4 8. 8 7. 0 9 4 7. 0 9. 3 8. 2 9. 7 Deep sadd1e 7. 9 8. 6 9. 7 8.2 9. 7 8. 4 9 6 8. 6 9. 5 8. 2 10. 4 9. 3 10. 4 Wear resistance, ft./rnrn.:

Standard 44.2 52.0 50.7 46.1 43.4 Deep saddle 64.1 67.3 70.8 62.8 52.3 48 7 *Resharpened after this hole.

result of such drilling and the necessary resharpening, 55

which as shown was after each fifteenth hole. The gures are therefore for the first hole drilled by a new bit, the hole just before resharpening and the hole immediately following resharpening and so on before and after each 2. The insert claimed in claim 1 in which the lands meet at least 0.019 inch below the shoulders.

3. The insert claimed in claim 1 in which the lands meet at between 0.019 inch and 0.080 inch below the shoulders.

4. The insert claimed in claim 3 in which the lands meet at 0.059 inch below the shoulders.

References Cited in the file of this patent UNITED STATES PATENTS 422,771 Grubbs Mar. 4, 1890 1,094,063 Forbes Apr. 21, 1914 2,707,619 Anderson v l May 3, 1955 

1. AN INSERT FOR A PRECUSSIVE ROCK DRILL BIT COMPRISING AN ELONGATED SUBSTANTIALLY RECTANGULAR PRISMATIC CONFIGURATION AND HAVING A FLAT BASE; TWO OPPOSED FLAT SIDES AT RIGHT ANGLES TO THE BASE; TWO OPPOSED SUBSTANTIALLY PARALLEL REAMING ENDS AT RIGHT ANGLES TO THE BASE AND THE LONG AXIS OF THE INSERT; AND A SUBSTANTIALLY CHISEL-SHAPED CUTTING FORMATION OPPOSED TO THE BASE, THE CUTTING FORMATION CONSISTING IN INCLINED CONCAVE LANDS MEETING AT A SHORT AXIS OF THE INSERT AND INTERSECTING THE FLAT SIDES, A CONCAVE CUTTING EDGE BEING FORMED WHERE THE CONCAVE LANDS MEET AND SUCH CUTTING EDGE BROADENING INTO A PAIR OF DIVERGENT TRIANGULAR FACES CONTINUOUS WITH AND HAVING THE SAME CONCAVITY AS THE CUTTING EDGE, AND A PAIR OF INCLINED SNUBS JOINING THE BASES OF THE TRIANGULAR FACES WITH THE REAMING ENDS, A SHOULDER BEING FORMED BY THE BASE OF EACH OF THE TRIANGULAR FACES MERGING WITH THE UPPEMOST PORTION OF EACH SNUB. 